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BIG PHYSICS, BIG QUESTIONS –

Pinpoint key ports to stop aquatic invaders

By Lakshmi Sandhana

Singapore sting

(Image: plainpicture/Sabine Vielmo)

TIME to flex our muscles against mussels. Since they first arrived in North America in 1988, zebra mussels have made themselves at home. The small molluscs, which attach themselves to boats and clog underwater pipes, cost the US billions of dollars in pipe cleaning and repair, lost hydroelectric power, damaged boat hulls and other headaches.

In a bid to stem the tide of invasive aquatic species like these, a team at the University of Notre Dame in Indiana have designed software to identify hubs in the global shipping network that have outsized roles in spreading interlopers. All told, invasive species are estimated to cost the US &dollar;120 billion a year.

The paths of ships, their ballast discharge, and ecological and environmental factors all influence the spread of species, says Nitesh Chawla, a leader of the project. By analysing all of these factors across hundreds of ports worldwide, the team has shown which places are the biggest spreaders of species and thus which would be best to target.

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“Singapore alone contributes to 26 per cent of total species flow among the 818 ports in the Pacific,” says Chawla.

Singapore contributes to 26 per cent of total species flow among the 818 ports in the Pacific

Asking every port to implement strict control measures, like testing and treating ballast water, could drag down productivity – but focusing on just those places most likely to spread invaders would have a large effect, say the researchers. “By assuming species-control policies were implemented on the top 20 per cent of the most connected ports, we showed that it would be at least twice as difficult for species to propagate,” says Chawla.

What’s more, says the team, container ships are more likely to transport invasive species than passenger carriers or barges. That means that in some areas, only large, bulk carriers need to be subject to the strictest inspection and prevention measures, and other ships can pass unhindered.

Kelly Pennington, who studies invasive species at the Minnesota Department of Natural Resources, says the work could inform global policies, and be adapted to the regional or state level as well.